1. Field of the Invention
The present invention relates to an imaging lens and, in particular, to an imaging lens suitable as a taking lens for a video camera or still video camera used for TV phone, door phone, monitoring purposes, or the like.
2. Description of the Prior Art
Recently, solid-state imaging devices have often been disposed on imaging surfaces of various kinds of video cameras and still video cameras. With the advance of technology, such solid-state imaging devices have been reducing their size year by year, while employing imaging lenses with smaller size and wider angle of view.
Conventionally known as the imaging lens used for the above-mentioned purposes is the one disclosed in Japanese Unexamined Patent Publication No. 8-5908 comprising four lens sheets and a stop disposed between the lenses.
In an imaging lens employed in a video camera or the like used for TV phone, door phone, monitoring purposes, and so forth, it is necessary for the whole lens system to have a small size in view of the space for its installation and the like.
When a stop is disposed between the lenses as in the imaging lens disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 8-5908 in the case where the stop function is to be provided within the lens system, however, a large space is necessary in front of and behind the stop, thus increasing the size of the whole lens system.
Hence, in order to reduce the size of the whole lens system, the stop may be disposed on the image side or object side of the lens system. When the stop is disposed on the image side of the lens system, however, in order to secure an exit pupil position, back focus has to be elongated more than necessary. Accordingly, when the stop function is to be provided within the lens system, it is preferable that the stop be positioned on the object side of the lens system.
When the stop is disposed on the object side of the lens system, however, various kinds of aberration, such as distortion in particular, may increase too much to be easily corrected.